1. Field of the Invention
The present invention relates to moving coil electrical instruments, and, more particularly, to a moving coil electrical meter mechanism, utilizing multiple magnetic flux filled air gaps to obtain increased indicator needle torque.
2. Description of the Prior Art
Moving coil meter mechanisms appearing in the prior art are of several basic types. The most common type is the basic D'Arsonval meter which utilizes a square or rectangular meter coil, one side of which is located in a magnetic flux filled air gap. The coil is typically mounted for rotation around an axis located outside the coil. (E.g., Lender, U.S. Pat. No. 3,040,253.) Also found in the prior art are meter mechanisms with square, rectangular or circular coils rotating on an axis corresponding to the axis of symmetry of the coil, with two symmetrical sides of the coil being located in magnetic flux filled air gaps. (E.g., Otzmann, U.S. Pat. No. 2,697,204.) A further type of meter mechanism found in the prior art has a square or rectangular coil mounted for rotation around an axis located outside the coil, with two symmetrical sides of the coil being located in flux-filled air gaps. (E.g., Faria, U.S. Pat. No. 3,490,043.) Still other meter mechanisms using somewhat more complicated configurations of coils and flux-filled air gaps are also known. (E.g., Nakata, U.S. Pat. No. 3,671,862.)
The chief disadvantage of each of these prior art meter mechanisms is the low indicator needle torque generated for a given meter volume. The reason for this disadvantage is that prior meter mechanism designs fail to optimally utilize the metering current flowing in the coil to produce rotational torque for the indicator needle. Typically, the geometry of the magnetic circuits used in prior art meter mechanisms utilizes current on one or, at most, two sides of the meter coil. Also, one or, at most, two magnetic circuits have been used to produce the magnetic flux which interacts with the coil current to provide the rotational torque.
The result of having low indicator needle torque for a given meter volume is that smaller meters, particularly, those suitable for use in aircraft control panels or other environments where space is at a premium, have unsatisfactory accuracy, damping and dynamic characteristics. Thus, with conventional meter mechanism designs there is a crucial trade-off between meter volume and the important performance characteristics of the meter mechanism.